Black piedra is caused by –
**Core Concept**
Black piedra is a rare fungal infection of the hair shaft, characterized by the formation of hard, dark-colored nodules on the hair. This condition is caused by a specific type of fungus that colonizes the hair shaft, leading to its degradation and the formation of these characteristic nodules.
**Why the Correct Answer is Right**
The fungus responsible for black piedra is Piedraia hortae. This fungus colonizes the hair shaft, producing a hard, melanin-like substance that accumulates and forms nodules. The infection is usually asymptomatic, but can cause discomfort and cosmetic concerns. The pathogenesis involves the attachment of the fungal spores to the hair shaft, followed by the formation of a biofilm that protects the fungus and allows it to proliferate.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a fungus that causes black piedra. While there are other fungi that infect the hair, Piedraia hortae is the specific species responsible for black piedra.
**Option B:** This option is incorrect because it refers to a different type of fungal infection that affects the scalp, rather than the hair shaft. Tinea capitis is a common fungal infection of the scalp, but it does not cause black piedra.
**Option C:** This option is incorrect because it refers to a type of bacterial infection that affects the skin, rather than a fungal infection of the hair. Staphylococcal infections can cause a range of skin conditions, but they are not associated with black piedra.
**Clinical Pearl / High-Yield Fact**
Black piedra is a rare but distinctive condition that should be considered in the differential diagnosis of hair shaft disorders. It is more common in warm and humid climates, and can be treated with antifungal medications.
**Correct Answer: D. Piedraia hortae**